RAID 5 is a storage configuration that uses block-level striping with distributed parity. It provides fault tolerance by distributing parity data across multiple disks. RAID 5 requires a minimum of three disks, with one disk’s worth of space used for parity storage. It was quite popular in the past for small- and medium-sized servers, as it provides a good balance between storage capacity, performance, and redundancy. However, changes in how data is accessed and stored have raised questions about whether RAID 5 is still a useful solution in modern IT environments.
What is RAID 5?
RAID (Redundant Array of Independent Disks) is a way of storing the same data across multiple hard disks to protect against disk failures. There are several different RAID levels, each offering different combinations of performance, capacity, and fault tolerance.
RAID 5 uses block-level striping, just like RAID 0, meaning data is broken up into blocks and spread evenly across all disks in the array. This provides performance improvements compared to a single disk, since multiple disks can be read from or written to simultaneously.
Unlike RAID 0, RAID 5 also provides fault tolerance by dedicating the equivalent of one disk’s worth of capacity for parity data. Parity is calculated based on the data being stored, and it is distributed across all the disks. If any single disk fails, the missing data can be recalculated using the parity information.
For example, in a 3-disk RAID 5 array, Disks 1 and 2 store user data while Disk 3 stores parity data. If Disk 2 fails, the data on it can be recalculated using the data on Disk 1 and the parity on Disk 3. This allows the RAID to continue operating with one failed drive (although there is no remaining redundancy until the failed drive is replaced).
The Pros of RAID 5:
Here are some of the benefits of using RAID 5:
- Good balance of storage capacity and redundancy – With only one disk worth of capacity used for parity, RAID 5 provides fault tolerance while still allowing for good storage utilization. A 3-disk RAID 5 array will have the usable capacity of 2 disks.
- Allows for one disk failure without data loss – Single disk fault tolerance allows a disk to fail without any data becoming inaccessible. The array can continue operating in a degraded state until the failed drive is replaced.
- Better random read performance than with a single disk – Spreading data across multiple disks allows for multiple read requests to be serviced simultaneously.
- Low cost of implementation – RAID 5 only requires a minimum of 3 disks, making it affordable to implement versus other RAID levels that require more disks.
- Easy to expand capacity – Disks can be added to a RAID 5 array to increase available storage.
For small servers and workstations that need some redundancy but don’t require massive amounts of storage, RAID 5 can provide an economical fault tolerance solution.
The Cons of RAID 5:
RAID 5 does have some drawbacks that need to be considered as well:
- Low write performance – Writes are slower because parity data needs to be calculated and written along with the main data being stored.
- No redundancy during rebuilds – If a second disk fails before a failed drive has been replaced, data loss will occur. The rebuild process itself also puts stress on the array.
- Large disk rebuilds – With today’s large SATA drives, rebuild times can be significant, putting the array at risk of a second disk failure during that time.
- Not optimized for virtualized environments – Features like snapshotting and cloning can impact performance.
- Limited scalability – Expanding a RAID 5 array requires a full parity rebuild, which takes a long time with large disk sizes.
While RAID 5 does provide basic redundancy, the performance penalties and risk of long rebuilds make it less ideal for mission critical data or large arrays.
Is RAID 5 Obsolete?
While RAID 5 has certainly decreased in popularity over the years, calling it completely obsolete may be an overstatement. Here are some key considerations when deciding if RAID 5 is still a viable solution:
- Disk sizes – Large SATA drives increase rebuild times. But if using smaller 2.5″ SSDs in the array, rebuild times are less concerning.
- Performance needs – RAID 5 still has merits for use cases that are not heavily write intensive and do not demand cutting edge speed.
- Cost – For budget constrained implementations, RAID 5 provides basic redundancy at a low cost.
- Array size – In smaller arrays, the rebuild weakness is less of a factor.
- Virtualization use – For lightly virtualized environments, RAID 5 may still suffice.
While alternatives like RAID 6 or RAID 10 may be better choices for mission critical systems, RAID 5 can still be a good fit for smaller scale implementations that need economy over peak performance and advanced features.
RAID 5 vs Other RAID Levels
To get a better idea of where RAID 5 fits in, here is how it compares to some other RAID options:
RAID 5 vs RAID 0
| Feature | RAID 5 | RAID 0 |
| Redundancy | Yes | No |
| Performance | Moderate read Slow write |
Fast read/write |
| Minimum disks | 3 | 2 |
| Capacity utilization | 1 disk for parity | 100% |
RAID 0 provides better performance but no redundancy. RAID 5 is slower but offers basic fault tolerance.
RAID 5 vs RAID 6
| Feature | RAID 5 | RAID 6 |
| Redundancy | 1 disk failure | 2 disk failures |
| Performance | Moderate read Slow write |
Slower than RAID 5 |
| Minimum disks | 3 | 4 |
| Capacity utilization | 1 disk for parity | 2 disks for parity |
RAID 6 can withstand the loss of 2 disks but at the cost of more overhead and loss of capacity. RAID 5 provides basic redundancy with lower overhead.
RAID 5 vs RAID 10
| Feature | RAID 5 | RAID 10 |
| Redundancy | 1 disk failure | 1 disk failure per mirrored pair |
| Performance | Moderate read Slow write |
Fast read/write |
| Minimum disks | 3 | 4 |
| Capacity utilization | 1 disk for parity | 50% |
RAID 10 provides significantly better performance while allowing for disk failures. But 50% of capacity is lost to redundancy.
When is RAID 5 Appropriate to Use?
Given its limitations, RAID 5 is no longer considered the default go-to RAID level it once was. But it can still be an appropriate solution in certain scenarios:
- Budget constrained environments – When cost is a major factor, RAID 5 provides basic redundancy at a low price point.
- Smaller disk sizes – With smaller SSDs or 2.5″ HDDs, rebuild times are less of a concern.
- Low I/O workloads – In use cases that don’t require heavy write performance and have smaller I/O block sizes, the RAID 5 write penalty is minimized.
- Virtualized mundane work – Lightly virtualized servers running mundane workloads like file and print sharing could still benefit from RAID 5’s basic redundancy.
- Short term needs – As a temporary solution until budget becomes available for something more robust like RAID 6 or RAID 10.
The key considerations are workload patterns and importance of the data. RAID 5 provides a baseline of redundancy that may be “good enough” for some use cases where cost savings and smaller capacity are beneficial.
Best Practices When Using RAID 5
If RAID 5 is determined to be suitable for a particular situation, here are some best practices to follow:
- Use smaller disks – Opt for 2.5″ SSDs or HDDs instead of larger 3.5″ drives to reduce rebuild times.
- Keep arrays small – Keep RAID 5 arrays to 8 disks or less to minimize the impact of rebuilds.
- Allow for spare drives – Having hot spare drives ready reduces the vulnerable period when a disk fails before a new one is installed.
- Monitor regularly – Watch for signs of impending disk failure and replace disks proactively rather than reactively.
- Ensure proper ventilation – Adequate airflow reduces disk heat buildup that can cause failures.
- Consider configuration risks – Improper RAID controller or firmware settings can exacerbate issues.
- Back up data – Don’t rely solely on any RAID as a backup. Maintain backups as an additional safety net.
Staying vigilant to minimize the likelihood of disk failure events in a RAID 5 array goes a long way towards ensuring its fault tolerance capabilities are there when needed.
Is RAID 5 Recommended for New Deployments?
For most general purpose use cases today, RAID 5 is no longer the first option I would recommend for new deployments. The performance penalties of RAID 5 along with the long rebuild times of larger drives make it less ideal compared to alternatives:
- RAID 10 – Preferred for performance sensitive applications, providing speed, redundancy, and rapid rebuilds. A good choice for virtualized environments.
- RAID 6 – Provides additional redundancy compared to RAID 5 while avoiding some of its pitfalls. A reasonable option for large arrays.
- Erasure Coding – More advanced schemes like Reed-Solomon coding offer distributed parity without RAID 5’s write penalty.
- Distributed File Systems – Systems like Ceph replicate and stripe data across multiple nodes. They provide redundancy without traditional RAID.
For mission critical data or high performance needs, one of these other options is likely a better fit than RAID 5. But in scenarios that require low cost redundancy and can tolerate slower rebuilds, RAID 5 may still be sufficient.
Conclusion
While RAID 5 is no longer considered the default standard it once was, it does still have usefulness in certain situations where cost savings and basic redundancy are the priorities. For less critical workloads in budget conscious environments, RAID 5 can be a “good enough” solution.
However, its performance penalties and extensive rebuilding times mean RAID 5 is ill-suited for more demanding production environments. New deployments focused on high availability will usually benefit more from RAID 10, RAID 6, or distributed erasure coding schemes. RAID 5 is best limited to smaller scale implementations with less intensive I/O needs.
By understanding both the capabilities and limitations of RAID 5, IT professionals can determine if it has a place in their infrastructure. While no longer a preferred choice in most scenarios, RAID 5 still fills a niche for cost-effective basic redundancy.
